Left 4 Dead uses the latest version of Valve's Source engine, with improvements such as multi-core processor support and physics-based animation to more realistically portray hair and clothing, and to improve physics interaction with enemies when shot or shoved in different body parts. Animation was also improved to allow characters to lean realistically when moving in curved paths.

Rendering and artificial intelligence were scaled up to allow for greater number of enemies who can navigate the world in better ways, such as climbing, jumping or breaking obstacles. Lighting has been enhanced with new self-shadowing normal mapping and advanced shadow rendering that is important to convey information about the environment and player actions.

HD 5870: There seems to be a small drop in performance, but nothing major and probably more a bit of fluctuation if anything.

HD 5850: Here we see no real change.

HD 4890: Like the HD 5870, we see a little drop in performance. Again, though, it isn't anything concerning.